On December 4, 2024 6:02:48 AM PST, Brian Gerst <brgerst@xxxxxxxxx> wrote: >On Wed, Dec 4, 2024 at 8:43 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: >> >> On Wed, Dec 4, 2024, at 14:29, Brian Gerst wrote: >> > On Wed, Dec 4, 2024 at 5:34 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote: >> >> >> >> - In the early days of x86-64 hardware, there was sometimes the need >> >> to run a 32-bit kernel to work around bugs in the hardware drivers, >> >> or in the syscall emulation for 32-bit userspace. This likely still >> >> works but there should never be a need for this any more. >> >> >> >> Removing this also drops the need for PHYS_ADDR_T_64BIT and SWIOTLB. >> >> PAE mode is still required to get access to the 'NX' bit on Atom >> >> 'Pentium M' and 'Core Duo' CPUs. >> > >> > 8GB of memory is still useful for 32-bit guest VMs. >> >> Can you give some more background on this? >> >> It's clear that one can run a virtual machine this way and it >> currently works, but are you able to construct a case where this >> is a good idea, compared to running the same userspace with a >> 64-bit kernel? >> >> From what I can tell, any practical workload that requires >> 8GB of total RAM will likely run into either the lowmem >> limits or into virtual addressig limits, in addition to the >> problems of 32-bit kernels being generally worse than 64-bit >> ones in terms of performance, features and testing. > >I use a 32-bit VM to test 32-bit kernel builds. I haven't benchmarked >kernel builds with 4GB/8GB yet, but logically more memory would be >better for caching files. > > >Brian Gerst > For the record, back when kernel.org was still a 32-bit machine which, once would have thought, would have been ideal for caching files, rarely achieved more than 50% memory usage with which I believe was 8 GB RAM. The next generation was 16 GB x86-64.
